Field of the Invention
The invention relates to a method for operation of a converter circuit, in particular a pulse-width modulated frequency converter circuit having a DC voltage intermediate circuit that controls two or more winding sections of a polyphase dynamo-electrical machine, in particular a three-phase asynchronous motor for a laundry appliance. The method determines one or more parameters of the dynamo-electrical machine. Furthermore, the invention relates to a converter circuit for carrying out the method and to a laundry appliance having a converter circuit for controlling a polyphase dynamo-electrical machine that, in particular, drives a drum that is mounted in the laundry appliance such that it can rotate.
Converter circuits and methods for operation of a converter circuit that control a dynamo-electrical machine are known in numerous forms from the prior art. Converter circuits are used for conversion of an input-side single-phase or polyphase AC voltage to an output-side single-phase or polyphase AC voltage, whose frequency, number of phases and/or amplitude differ from the input-side AC voltage. Converter circuits that can convert the frequency of an AC voltage, so-called frequency converter circuits or frequency change circuits, can produce any desired voltage frequencies and/or voltage amplitudes on the output side. Frequency converter circuits are also used to control the rotation speed of dynamo-electrical machines, for example three-phase asynchronous motors. Asynchronous motors such as these require extremely little maintenance, have high power limits and can be operated with particularly little noise. Owing to these advantages, dynamo-electrical machines such as these whose rotation speed is regulated are also used in laundry appliances, such as domestic washing machines or domestic washer/driers. Machines such as these are used to drive, for example, a washing drum that is mounted in the laundry appliance such that it can rotate. In this case, pulse-width modulated frequency converter circuits are used, in particular, in order to control three-phase asynchronous motors. The components of frequency converter circuits such as these generally each include a mains filter, a DC voltage intermediate circuit, a power stage with a so-called driver stage, and a microcontroller or a digital signal processor. The components are generally combined in an assembly, in which case, for example, the mains filter may form a separate assembly. In addition to the components mentioned above, converter circuits for open-loop and/or closed-loop control of dynamo-electrical machines also use sensor elements for detection of the voltage, current, and/or temperature in the converter circuit, and/or devices for detection of parameters relating to the driven dynamo-electrical machine. The parameters may vary, particularly as a result of heating during operation of the machine. Sensor elements or devices such as these are in some cases integral assemblies within the converter circuit and are used for power-optimized operation of the dynamo-electrical machine. The detected currents, voltage, temperature value, and/or the machine parameters can be used in conjunction with individual calculation rules or complex mathematical machine models for the microcontroller or digital signal processor to determine closed-loop and/or open-loop control variables, which result in the machine being driven in a power-optimized manner in every operating state of the machine.
Known converter circuits may have a technically complex and costly construction and, in some cases, are susceptible to defects. Further devices are required for protection of the converter circuit and/or of the dynamo-electrical machine to disconnect the converter circuit during an overvoltage, an overtemperature, a short-circuit, a ground short, and/or a turns short in the frequency converter circuit and/or in the dynamo-electrical machine.
When using a dynamo-electrical machine with a converter circuit in a laundry appliance, in particular in a domestic washing machine or in a domestic washer/drier, the protective devices ensure compliance with the regulations of the international electrical standards that are applicable to a laundry appliance. In this case, even in the event of malfunctions and/or faults of individual components, such as the converter circuit and/or the dynamo-electrical machine in the laundry appliance, no hazards may result, for example as a result of excessive component heating, overcurrents, and line shorts for the operator of the laundry appliance. The protective devices that have been used in laundry appliances until now admittedly result in reliable compliance within the specified standards, but in some cases the protective devices are costly and do not ensure sufficient preventative protection against a component defect resulting in a repair to the laundry appliance.